This invention relates to an ink jet printing process for improving the dye density and fixability of an ink jet image ink containing a water-soluble cationic or basic dye.
Ink jet printing is a non-impact method for producing images by the deposition of ink droplets in a pixel-by-pixel manner to an image-recording element in response to digital signals. There are various methods which may be utilized to control the deposition of ink droplets on the image-recording element to yield the desired image. In one process, known as continuous ink jet, a continuous stream of droplets is charged and deflected in an imagewise manner onto the surface of the image-recording element, while unimaged droplets are caught and returned to an ink sump. In another process, known as drop-on-demand ink jet, individual ink droplets are projected as needed onto the image-recording element to form the desired image. Common methods of controlling the projection of ink droplets in drop-on-demand printing include piezoelectric transducers and thermal bubble formation. Inkjet printers have found broad applications across markets ranging from industrial labeling to short run printing to desktop document and pictorial imaging.
The inks used in the various ink jet printers can be classified as either dye-based or pigment-based. A dye is a colorant which is molecularly dispersed or solvated by a carrier medium. The carrier medium can be a liquid or a solid at room temperature. A commonly used carrier medium is water or a mixture of water and organic co-solvents. Each individual dye molecule is surrounded by molecules of the carrier medium. In dye-based inks, no particles are observable under the microscope. Although there have been many recent advances in the art of dye-based ink jet inks, such inks still suffer from deficiencies such as low optical densities on plain paper and poor light-fastness. When water is used as the carrier medium, such inks also generally suffer from poor water-fastness.
The ink jet receiving elements that can be used with the above mentioned inks must meet several requirements including producing high density images that will not smear, bleed or wander when exposed to water for short periods of time.
U.S. Pat. No. 5,560,996 relates to the use of a printing paper containing an intercalated compound that can chemically fix water soluble, cationic or anionic dyes to the paper by an electrostatic attraction between the dye and the intercalated compound. Although this type of an ink receiving layer does provide an image with good fixability, there is a problem with this material in that the overall density of the images generated is too low, as will be shown hereafter.
It is an object of this invention to provide an ink jet printing process for improving the fixability of an ink jet image so that it does not smear or wander when subjected to water for a period of time. It is another object of this invention to provide an ink jet printing process wherein the ink jet image is of high density.
These and other objects are achieved in accordance with the present invention which comprises an ink jet printing process for improving the dye density and fixability of an ink jet image comprising:
a) providing an ink jet recording element comprising a support having thereon an image-recording layer comprising a mixture of an anionic, addition polymer and a hydrophilic polymer; and
b) applying droplets of a liquid ink on the image-recording layer in an image-wise manner, the ink comprising water, humectant and a water-soluble cationic or basic dye.
It was found that the fixability of the printed ink jet image is of high density and does not smear or wander when subjected to water for a period of time.
A variety of basic or cationic dyes may be used in the invention as disclosed in U.S. Pat. No. 5,560,996, the disclosure of which is hereby incorporated by reference. In a preferred embodiment of the invention, the dye is an azo dye, a triphenylmethane dye, a phthalocyanine dye, an azine dye, an oxazine dye, a thiazine dye, each having an amine salt residue or a quaternary ammonium group. Such inks may be prepared directly from the basic or cationic dyes or by redissolving the leuco or deprotonated, electrically neutral forms (precursor) of these dyes in dilute aqueous acids, as described in U.S. Pat. Nos. 4,880,769; 3,992,140; and 5,559,076 and U.S. Ser. Nos. 09/299,480 and 09/299,412, both filed Apr. 26, 1999, the disclosures of which are hereby incorporated by reference. Examples of such electrically neutral forms of cationic dyes include the following: 
The dyes described above may be employed in any amount effective for the intended purpose. In general, good results have been obtained when the dye is present in an amount of from about 0.2 to about 5% by weight of the ink jet ink composition, preferably from about 0.3 to about 3% by weight. Dye mixtures may also be used.
In a preferred embodiment of the invention, the anionic, addition polymers have the following general formula 
wherein:
R1 represents H, CH3 or CH2CO2R4;
R2 represents H or CO2R4;
R3 represents CO2R4, PO3(R4)2, Ar(CO2R4)x, Ar(SO3R4)x, Ar(O R4)y(SO3R4)x, Ar(PO3(R4)2)x, CO2xe2x80x94R5xe2x80x94CO2R4, CO2xe2x80x94R5xe2x80x94SO3R4, CO2xe2x80x94R5xe2x80x94PO3(R4)2, COxe2x80x94NHxe2x80x94R5xe2x80x94CO2R4, COxe2x80x94NHxe2x80x94R5xe2x80x94SO3R4, COxe2x80x94NHxe2x80x94R5xe2x80x94PO3(R4)2;
R4 represents H, an alkali or alkaline earth metal ion, or an ammonium or substituted ammonium ion;
x and y each independently represents an integer from 0 to 3;
Ar represents an aryl group of from about 6 to about 10 carbon atoms or a hetaryl group of from about 5 to about 10 atoms; and
R5 represents a straight-chain or branched alkyl, aryl or alkylene oxide group having 10 carbon atoms or less;
Z represents at least one ethylenically unsaturated monomer;
m represents a mole % of from about 5 to about 100; and
n represents a mole % of from about 95 to 0.
Comonomers Z useful in this invention include a large number of ethylenically unsaturated monomers capable of undergoing addition polymerization with the other monomer providing the repeat unit above under the reaction conditions employed. Z may be selected from the styrenics, e.g., styrene, alpha alkylstyrene where the alkyl group has 1 to 4 carbon atoms and the aromatic group may be substituted or part of a larger ring system. Other examples of Z include acrylate esters derived from aliphatic alcohols or phenols; methacrylate esters; acrylamides; methacrylamides; N-vinylpyrrolidone or suitably substituted vinylpyrrolidones; vinyl esters derived from straight chain and branched acids, e.g., vinyl acetate; vinyl ethers, e.g., vinyl methyl ether; vinyl nitriles; vinyl ketones; halogen-containing monomers such as vinyl chloride; and olefins, such as butadiene.
The polymers of this invention can be prepared using conventional polymerization techniques including, but not limited to bulk, solution, emulsion, or suspension polymerization. They also can be partially crosslinked.
Examples of anionic, addition polymers useful in the invention include the following:
P-1: poly(styrene-co-butyl methacrylate-co-2-sulfoethyl methacrylate sodium salt) 30:60:10 mole ratio
P-2: poly(styrene-co-butyl methacrylate-co-2-acrylamido-2-methylpropanesulfonic acid, sodium salt) 30:60:10 mole ratio
P-3: poly(styrene-co-butyl methacrylate-co-acrylic acid sodium salt) 30:60:10 mole ratio
P-4: poly(styrene-co-butyl methacrylate-co-itaconic acid sodium salt) 30:60:10 mole ratio
P-5: poly(styrene-co-butyl methacrylate-co-aconitic acid sodium salt) 30:60:10 mole ratio
P-6: CP615NA (carboxylated styrene butadiene copolymer from Dow Chemical Company)
P-7: XU31066.50 (experimental polymer based on styrene butadiene copolymer from Dow Chemical Company)
P-8: poly(acrylamide-co-2-acrylamido-2-methylpropanesulfonic acid, sodium salt) 90:10 mole ratio
P-9: poly(acrylamide-co-2-acrylamido-2-methylpropanesulfonic acid, sodium salt) 10:90 mole ratio
P-10: poly(acrylamide-co-acrylic acid sodium salt) 50:50 mole ratio
P-11: poly(acrylamide-co-acrylic acid sodium salt) 10:90 mole ratio
P-12: poly(styrene-co-butyl methacrylate-co-4-styrene sulfonic acid, sodium salt) 30:60:10 mole ratio
P-13: poly(styrene-co-butyl methacrylate-co-4-styrene sulfonic acid, sodium salt) 30:40:30 mole ratio
P-14: poly(acrylamide-co-2-carboxyethyl acrylate) 25/75 mole ratio
P-15: poly(acrylamide-co-2-carboxyethyl acrylate) 60/40 mole ratio
P-16: poly(acrylamide-co-2-carboxyethyl acrylate) 75/25 mole ratio
P-17: poly(2-carboxyethyl acrylate)
The addition polymer employed in the invention may be used in an amount of from about 0.2 to about 26 g/m2, preferably from about 1 to about 16 g/m2.
Any hydrophilic polymer may be used in the invention. For example, there may be used gelatin or polymers having the following formula: 
wherein:
R6 represents hydrogen or an alkyl group having from about 1 to about 6 carbon atoms; and
R7 represents hydroxyl, pyrrolidone, NHCOR8 or CONHR8, where R8 represents an alkyl group having from about 1 to about 6 carbon atoms.
Examples of the above hydrophilic polymer include polyvinyl alcohol, polyvinyl pyrrolidone, poly(ethyl oxazoline), non-deionized or deionized Type IV bone gelatin, acid processed ossein gelatin or pig skin gelatin. The hydrophilic polymer may be present in an amount of from about 0.4 to about 30 g/m2, preferably from about 1 to about 16 g/m2.
Examples of hydrophilic polymers which may be used in this invention include:
G-1: Type IV non-deionized bone gel, isoelectric point=5.0 (Eastman Chemical Co.)
G-2: Acid Processed Ossein gel, isoelectric point=6.7 (Croda Colloids Ltd.)
G-3: Pig skin deionized gel, isoelectric point=8.0 (SKW Biosystems).
In a preferred embodiment of the invention, the weight ratio of anionic, addition polymer to hydrophilic polymer is from about 1:9 to about 8:2, preferably from about 1 to about 1.
The pH of the aqueous ink compositions of the invention may be adjusted by the addition of organic or inorganic acids or bases. Useful inks may have a preferred pH of from about 2 to 7, depending upon the type of dye being used. Typical inorganic acids include hydrochloric, phosphoric and sulfuric acids. Typical organic acids include methanesulfonic, acetic and lactic acids. Typical inorganic bases include alkali metal hydroxides and carbonates and ammonia. Typical organic bases include triethanolamine and tetramethylethylenediamine.
A humectant is employed in the ink jet composition of the invention to help prevent the ink from drying out or crusting in the orifices of the printhead. Examples of humectants which can be used include polyhydric alcohols, such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, tetraethylene glycol, polyethylene glycol, glycerol, 2-methyl-2,4-pentanediol, 1,2,6-hexanetriol and thioglycol; lower alkyl mono- or di-ethers derived from alkylene glycols, such as ethylene glycol mono-methyl or mono-ethyl ether, diethylene glycol mono-methyl or mono-ethyl ether, propylene glycol mono-methyl or mono-ethyl ether, triethylene glycol mono-methyl or mono-ethyl ether, diethylene glycol di-methyl or di-ethyl ether, and diethylene glycol monobutylether; nitrogen-containing cyclic compounds, such as pyrrolidone, N-methyl-2-pyrrolidone, and 1,3-dimethyl-2-imidazolidinone; and sulfur-containing compounds such as dimethyl sulfoxide and tetramethylene sulfone. A preferred humectant for the composition of the invention is diethylene glycol, glycerol, or diethylene glycol monobutylether.
Water-miscible organic solvents may also be added to the aqueous ink of the invention to help the ink penetrate the receiving substrate, especially when the substrate is a highly sized paper. Examples of such solvents include alcohols, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, t-butyl alcohol, iso-butyl alcohol, furfuryl alcohol, and tetrahydrofurfuryl alcohol; ketones or ketoalcohols such as acetone, methyl ethyl ketone and diacetone alcohol; ethers, such as tetrahydrofuran and dioxane; and esters, such as, ethyl lactate, ethylene carbonate and propylene carbonate.
Surfactants may be added to adjust the surface tension of the ink to an appropriate level. The surfactants may be anionic, cationic, amphoteric or nonionic. A preferred surfactant for the ink composition of the present invention is Surfynol(copyright) 465 (Air Products) at a final concentration of 0.1% to 1.0%.
A biocide may be added to the composition of the invention to suppress the growth of micro-organisms such as molds, fungi, etc. in aqueous inks. A preferred biocide for the ink composition of the present invention is Proxel(copyright) GXL (Zeneca Specialties Co.) at a final concentration of 0.05-0.5 wt. %.
A typical ink composition of the invention may comprise, for example, the following substituents by weight: colorant (0.2-5%), water (20-95%), humectant (5-70%), water miscible co-solvents (2-20%), surfactant (0.1-10%), biocide (0.05-5%) and pH control agents (0.1-10%).
Additional additives which may optionally be present in the ink jet ink composition of the invention include thickeners, conductivity enhancing agents, anti-kogation agents, drying agents, and defoamers.
The image-recording layer used in the process of the present invention can also contain various known additives, including matting agents such as titanium dioxide, zinc oxide, silica and polymeric beads such as crosslinked poly(methyl methacrylate) or polystyrene beads for the purposes of contributing to the non-blocking characteristics and to control the smudge resistance thereof; surfactants such as non-ionic, hydrocarbon or fluorocarbon surfactants or cationic surfactants, such as quaternary ammonium salts; fluorescent dyes; pH controllers; anti-foaming agents; lubricants; preservatives; viscosity modifiers; dye-fixing agents; waterproofing agents; dispersing agents; UV-absorbing agents; mildew-proofing agents; mordants; antistatic agents, anti-oxidants, optical brighteners, and the like. A hardener may also be added to the ink-receiving layer if desired.
The support for the ink jet recording element used in the invention can be any of those usually used for ink jet receivers, such as paper, resin-coated paper, poly(ethylene terephthalate), poly(ethylene naphthalate) and microporous materials such as polyethylene polymer-containing material sold by PPG Industries, Inc., Pittsburgh, Pa. under the trade name of Teslin(copyright), Tyvek(copyright) synthetic paper (DuPont Corp.), and OPPalyte(copyright) films (Mobil Chemical Co.) and other composite films listed in U.S. Pat. No. 5,244,861.
The support used in the invention may have a thickness of from about 50 to about 500 xcexcm, preferably from about 75 to 300 xcexcm. Antioxidants, antistatic agents, plasticizers and other known additives may be incorporated into the support, if desired. In a preferred embodiment, paper is employed.
In order to improve the adhesion of the image-recording layer to the support, the surface of the support may be subjected to a corona-discharge-treatment prior to applying the image-recording layer.
In addition, a subbing layer, such as a layer formed from a halogenated phenol or a partially hydrolyzed vinyl chloride-vinyl acetate copolymer can be applied to the surface of the support to increase adhesion of the image recording layer. If a subbing layer is used, it should have a thickness (i.e., a dry coat thickness) of less than about 2 xcexcm.
The image-recording layer may be present in any amount which is effective for the intended purpose. In general, good results are obtained when it is present in an amount of from about 2 to about 33 g/m2, preferably from about 6 to about 16 g/m2, which corresponds to a dry thickness of about 2 to about 30 xcexcm, preferably about 6 to about 15 xcexcm.
The following examples are provided to illustrate the invention.